<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>$课堂练习$</title>
    <style>
        ul {
            list-style: none;
            cursor: pointer;
        }
    </style>
</head>
<body>
<ul id="uu">
    <li>哈哈</li>
    <li>哈哈</li>
    <li>哈哈</li>
    <li>哈哈</li>
    <li>哈哈</li>
</ul>
<script src="common.js"></script>
<script>
    var list = my$("uu").getElementsByTagName("li");
    for (var i = 0; i < list.length; i++) {
        list[i].onmouseover = function () {
            this.style.backgroundColor = "red";
        }
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            this.style.backgroundColor = "";
        };
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    ;
</script>
</body>
</html>